1. Field of the Invention
This invention relates to a plasma display panel, and more particularly to a method and apparatus of driving a plasma display panel that is adaptive for making a stable operation at both a low temperature and a high temperature.
2. Description of the Related Art
Generally, a plasma display panel (PDP) excites and radiates a phosphorus material using an ultraviolet ray generated upon discharge of an inactive mixture gas such as He+Xe, Ne+Xe or He+Ne+Xe, to thereby display a picture. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development.
Referring to FIG. 1, a discharge cell of a conventional three-electrode, AC surface-discharge PDP includes a sustain electrode pair having a scan electrode 30Y, a common sustain electrode 30Z provided on an upper substrate 10, and an address electrode 20X provided on a lower substrate 18 in such a manner to perpendicularly cross the sustain electrode pair. Each of the scan electrode 30Y and the common sustain electrode 30Z has a structure disposed with transparent electrodes 12Y and 12Z and metal bus electrodes 13Y and 13Z thereon. On the upper substrate 10 provided, in parallel, with the scan electrode 30Y and the common sustain electrode 30Z, an upper dielectric layer 14 and an MgO protective film 16 are disposed. A lower dielectric layer 22 and barrier ribs 24 are formed on the lower substrate 18 provided with the address electrode 20X, and a phosphorous material layer 26 is coated onto the surfaces of the lower dielectric layer 22 and the barrier ribs 24. An inactive mixture gas such as He+Xe, Ne+Xe or He+Ne+Xe is injected into a discharge space among the upper substrate 10, the lower substrate 18 and the barrier ribs 24.
Such a PDP makes a time-divisional driving of one frame, which is divided into various sub-fields having a different emission frequency, so as to realize gray levels of a picture. Each sub-field is again divided into an initialization period for initializing the entire field, an address period for selecting a scan line and selecting the cell from the selected scan line and a sustain period for expressing gray levels depending on the discharge frequency. The initialization period is divided into a set-up interval supplied with a rising ramp waveform and a set-down interval supplied with a falling ramp waveform.
For instance, when it is intended to display a picture of 256 gray levels, a frame interval equal to 1/60 second (i.e. 16.67 msec) is divided into 8 sub-fields SF1 to SF8 as shown in FIG. 2. Each of the 8 sub-field SF1 to SF8 is divided into an initialization period, an address period and a sustain period as mentioned above. Herein, the initialization period and the address period of each sub-field are equal for each sub-field, whereas the sustain period and the number of sustain pulses assigned thereto are increased at a ratio of 2n (wherein n=0, 1, 2, 3, 4, 5, 6 and 7) at each sub-field.
FIG. 3 shows a driving waveform of the PDP applied to two sub-fields. Herein, Y represents the scan electrode; Z does the common sustain electrode; and X does the address electrode.
Referring to FIG. 3, the PDP is divided into an initialization period for initializing the full field, an address period for selecting a cell, and a sustain period for sustaining a discharge of the selected cell for its driving.
In the initialization period, a rising ramp waveform Ramp-up is simultaneously applied all the scan electrodes Y in a set-up interval SU. A discharge is generated within the cells at the full field with the aid of the rising ramp waveform Ramp-up. By this set-up discharge, positive wall charges are accumulated onto the address electrode X and the sustain electrode Z while negative wall charges are accumulated onto the scan electrode Y. In a set-down interval SD, a falling ramp waveform Ramp-down falling from a positive voltage lower than a peak voltage of the rising ramp waveform Ramp-up is simultaneously applied to the scan electrodes Y after the rising ramp waveform Ramp-up was applied. The falling ramp waveform Ramp-down causes a weak erasure discharge within the cells to erase a portion of excessively formed wall charges. Wall charges enough to generate a stable address discharge are uniformly left within the cells with the aid of the set-down discharge.
In the address period, a negative scanning pulse scan is sequentially applied to the scan electrodes Y and, at the same time, a positive data pulse data is applied to the address electrodes X in synchronization with the scanning pulse scan. A voltage difference between the scanning pulse scan and the data pulse data is added to a wall voltage generated in the initialization period to thereby generate an address discharge within the cells supplied with the data pulse data. Wall charges enough to cause a discharge when a sustain voltage is applied are formed within the cells selected by the address discharge.
Meanwhile, a positive direct current voltage Zdc is applied to the common sustain electrodes Z during the set-down interval and the address period. The direct current voltage Zdc causes a set-down discharge between the common sustain electrode Z, and allows an address discharge generated between the scan electrode Y and the address electrode X in the address period to be transited into a surface discharge between the scan electrode Y and the common sustain electrode Z.
In the sustain period, a sustaining pulse sus is alternately applied to the scan electrodes Y and the common sustain electrodes Z. Then, a wall voltage within the cell selected by the address discharge is added to the sustain pulse sus to thereby generate a sustain discharge, that is, a display discharge between the scan electrode Y and the common sustain electrode Z whenever the sustain pulse sus is applied.
Finally, after the sustain discharge was finished, a ramp waveform erase having a small pulse width and a low voltage level is applied to the common sustain electrode Z to thereby erase wall charges left within the cells of the entire field.
However, such a conventional PDP has a problem in that a brightness point mis-discharge or no discharge occurs at a high temperature (i.e., more than 40° C.) and a low temperature (i.e., approximately 20° C. to −50° C.) upon driving. More specifically, when the PDP is driven at a high temperature atmosphere more than about 40° C. with being divided into a first half and a second half as shown in FIG. 4, that is, by a double scan strategy, there is raised a problem in that no address discharge occurs at the middle portion 41 of the screen having a late scanning sequence. Likewise, when the PDP is scanned at a high temperature atmosphere more than about 40° C. sequentially from the first line until the last line as shown in FIG. 5, that is, by a single scan strategy, there is raised a problem in that no address discharge occurs at the lower portion 51 of the screen having a late scanning sequence.
As a result of many experiments and analyses as to the experiments, a major factor causing a misfire at a high temperature atmosphere is because a loss amount of wall charges generated in the initialization period is more increased as a scanning sequence is later. Such a factor will be described on a basis of a discharge characteristic change within the cell below. Firstly, as an internal/external temperature of the cell rises, wall charges are lost due to a leakage current generated from deterioration in an insulation property of a dielectric material and a protective layer within the cell. Secondary, as a motion of space charges within the cell is more activated, a re-combination of the space charges with atoms having lost electrons is easily generated. Thus, wall charges and space charges contributed to the discharge are lost with the lapse of time.
Furthermore, when the PDP is driven at a low temperature atmosphere less than 20° C., a motion of particles becomes dull to generate a brightness point misfire. More specifically, if a motion of particles becomes dull at a low temperature, then an erasure discharge caused by an erasing ramp waveform erase is not normally generated. Wall charges formed at the scan electrode Y and the common sustain electrode Z are not erased from the cells having such an abnormal erasure discharge.
Thereafter, a positive rising ramp waveform Ramp-up is applied to the scan electrode Y in the set-up interval. At this time, since negative wall charges has been formed at the scan electrode Y, that is, since a voltage applied to the scan electrode Y and wall charges having been formed at the scan electrode Y has an opposite polarity with respect to each other, a normal discharge is not generated in the set-up interval. Further, in the set-down interval following the set-up interval, a normal discharge is not generated. If a normal discharge does not occur in the initialization period, then wall charges formed excessively in the erasure period make an affect to the address period and the sustain period. In other words, wall charges formed excessively at the discharge cells cause an undesired strong discharge taking a brightness point shape in the sustain period.